Nucleic acid sequences encoding modified prepro peptides of an alkaline protease

ABSTRACT

The present invention relates to genes expressing an alkaline protease having a prepro sequence, vectors containing the same, and transformants containing said vector. The present invention also relates to a method for producing an alkaline protease.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. application Ser. No. 10/456,479, filed on Jun. 9, 2003, which issued as U.S. Pat. No. 7,101,698 on Sep. 5, 2006, and which claims priority to JP 2002-186387, filed on Jun. 26, 2002 and JP 2002-304232, filed on Oct. 18, 2002.

TECHNICAL FIELD

The present invention relates to an alkaline protease that is useful as an enzyme to be incorporated into a detergent.

BACKGROUND ART

Among proteases, alkaline proteases to be incorporated into detergents such as laundry detergents are produced in the greatest amounts in the industrial field. Examples of such alkaline proteases known heretofore include Alcalase (registered trademark; Novozymes), Savinase (registered trademark; Novozymes), Maxacal (registered trademark; Genencor), Blap (registered trademark; Henkel), and KAP (Kao Corporation).

Protease is incorporated into a laundry detergent for providing the detergent with the ability to degrade protein soils deposited on clothing. However, actual soils deposited on clothing are complex soils containing, in addition to proteins, a plurality of organic and inorganic components such as sebum-derived lipid, mud, and dust. Therefore, demand has arisen for a detergent exhibiting excellent detergency against such complex soils.

In view of the foregoing, the present inventors have previously found several alkaline proteases having a molecular weight of about 43,000 which maintain sufficient casein-degrading activity even in the presence of fatty acids of high concentrations and which exhibit excellent detergency against complex soils containing proteins and sebum and have previously filed a patent application on the alkaline proteases (see International Publication WO99/18218). These alkaline proteases differ from conventionally known subtilisin, a serine protease derived from bacteria belonging to the genus Bacillus, in molecular weight, primary structure, and enzymological characteristics, particularly in having very strong oxidant resistance. Thus, it has been suggested that these alkaline proteases be classified into a new subtilisin subfamily (see Saeki, et al., Biochem. Biophys. Res. Commun., 279, (2000), 313–319).

However, the production amount of such proteases may be insufficient for industrial-scale production, and thus demand has arisen for an alkaline protease which is efficiently produced in a culture medium.

Meanwhile, in order to produce a large amount of the target protein (enzyme), attempts have been made to improve host bacteria (host strains) through mutation breeding, or to modify the gene encoding the enzyme or the gene controlling the expression of the enzyme, thereby enhancing secretion of the enzyme. However, no attempt has been made to enhance secretion of subtilisin by modifying the prepro sequence thereof, which plays an important role in generation and folding.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an alkaline protease having a prepro sequence, wherein the prepro sequence is a mutated sequence of the amino acid sequence of SEQ ID NO: 1 or an amino acid sequence having 80% or higher homology to the amino acid sequence of SEQ ID NO: 1, in which amino acid residues at (a) position 52, (b) position 75, and (c) position 142 of SEQ ID NO:1, or amino acid residues at positions corresponding to these positions are substituted by the following amino acid residues:

-   -   at position (a): aspartic acid or arginine,     -   at position (b): alanine or arginine, and     -   at position (c): lysine;         and the alkaline protease, when in a mature form, has the amino         acid sequence of SEQ ID NO: 2 or an amino acid sequence having a         homology of 80% or higher to this amino acid sequence. The         present invention also provides a structural gene encoding the         alkaline protease; a vector harboring the structural gene; and a         transformant comprising the vector.

The present invention also provides a gene encoding the aforementioned mutant prepro sequence.

The present invention also provides a method for producing an alkaline protease having the amino acid sequence of SEQ ID NO: 2, or an amino acid sequence having a homology of 80% or higher to this amino acid sequence, which method comprises employing the aforementioned transformant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in a side-by-side manner of representation, a prepro sequence consisting of the amino acid sequence of SEQ ID NO: 1 and prepro sequences consisting of amino acid sequences having a homology of 80% or higher to this amino acid sequence. In FIG. 1, the order of sequences shown, from top to bottom, are SEQ ID NOs: 1, 8, and 9.

FIGS. 2 a and 2 b show, in a side-by-side manner of representation, a protease having the amino acid sequence of SEQ ID NO: 2 and proteases having amino acid sequences having a homology of 80% or higher to this amino acid sequence. FIG. 2 b is a continuation of FIG. 2 a. In FIG. 2, the order of sequences shown, from top to bottom, are SEQ ID NOs: 2 and 10–16.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have conducted investigations on a novel enzyme which maintains the aforementioned characteristics of the alkaline protease and is efficiently produced in a culture medium, and have found that, when an amino acid residue at a specific position of the prepro sequence of the alkaline protease is replaced with a specific amino acid residue, productivity of the alkaline protease can be enhanced.

The prepro sequence of the alkaline protease of the present invention (which may be referred to as “mutant prepro sequence”) is a modified (or mutated) sequence of the amino acid sequence of SEQ ID NO: 1 or an amino acid sequence having 80% or higher homology to the amino acid sequence of SEQ ID NO: 1, in which amino acid residues at position 52 (may be referred to as position (a)), position 75 (may be referred to as position (b)), and position 142 (may be referred to as position (c)) of SEQ ID NO:1 or amino acid residues at positions corresponding to these positions are substituted by the following amino acid residues:

-   -   at position (a): aspartic acid or arginine,     -   at position (b): alanine or arginine, and     -   at position (c): lysine.         In the present invention, the prepro sequence may be a wild-type         mutant sequence or an artificially mutated sequence.

The prepro sequence is a critical region relating to secretion and folding of the alkaline protease. The pre-sequence is a signal sequence, and is cleaved by signal peptidase when an alkaline protease precursor passes through a cell membrane. Meanwhile, the pro-sequence is known to act as an intramolecular chaperonin, and is an essential region for providing the alkaline protease with a correct three-dimensional structure before and after it passes through a cell membrane. The pro-sequence is finally cleaved by mature alkaline protease, and is degraded into small peptides. A product obtained through transcription and translation of the structural gene encoding the alkaline protease is present in a cell in the form of an alkaline protease precursor having a prepro sequence. Therefore, the alkaline protease having a prepro sequence of the present invention refers to an alkaline protease precursor.

Examples of the amino acid sequence of SEQ ID NO: 1; i.e., a non-mutated prepro sequence, include the prepro sequence of KP43 [derived from Bacillus sp. KSM-KP43 (FERM BP-6532), International Publication WO99/18218].

Among amino acid sequences having a homology of 80% or higher to the amino acid sequence of SEQ ID NO: 1, preferred are those having a homology of 87% or higher, more preferably 90% or higher, still more preferably 95% or higher, even still more preferably 98% or higher. Amino acid sequences having 80% or higher homology to the amino acid sequence of SEQ ID NO: 1 are preferably prepro sequences of an alkaline protease consisting of an amino acid sequence having a homology of 80% or higher to the amino acid sequence of SEQ ID NO:2 described below. Specific examples of such an amino acid sequence include the prepro sequence of protease KP9860 (GenBank Accession No. AB046403) [derived from Bacillus sp. KSM-KP9860 (FERM BP-6534), International Publication WO99/18218], and the prepro sequence of protease 9865 (GenBank Accession No. AB084155) [derived from Bacillus sp. KSM-9865 (FERM P-18566), Japanese Patent Application No. 2002-2653]. The homologies of the prepro sequences of protease KP9860 and protease 9865 to the amino acid sequence of SEQ ID NO: 1 are 86.8% and 97.6%, respectively (FIG. 1).

The homology between amino acid sequences is calculated by means of programs such as GENETYX WIN maximum matching or search homology (products of Software Development Co., Ltd.).

“Amino acid residues at positions corresponding to these positions” can be identified by comparing amino acid sequences of alkaline proteases by means of a known algorithm such as the Lipman-Person method, to thereby assign maximum homology to conserved amino acid residues present in the amino acid sequence of each alkaline protease. When the amino acid sequences of the prepro sequences are aligned by means of such a method, the positions of the homologous amino acid residues in each of the prepro sequences can be determined regardless of insertion or deletion of amino acid residue(s) in the amino acid sequences. Conceivably, the homologous amino acid residues are located at the same positions in the three-dimensional structures of the prepro sequences, and thus the alkaline proteases having the prepro sequences are analogous in terms of specificity-related functions.

As shown in FIG. 1, in which amino acid sequences are aligned by means of the aforementioned method, the amino acid residues at (a) position 52, (b) position 75, and (c) position 142 of SEQ ID NO: 1 are lysine, glutamine, and glutamic acid, respectively. The amino acid residues at positions corresponding to positions (a) through (c) can be identified by means of the aforementioned method. For example, in the prepro sequence of protease KP9860 or protease 9865, the amino acid residues at (a) position 52, (b) position 75, and (c) position 142 are lysine, glutamine, and glutamic acid, respectively.

In the mutant prepro sequence of the alkaline protease of the present invention, the amino acid residue at (a) position 52 of SEQ ID NO: 1 or at a position corresponding to this position is preferably substituted by aspartic acid or arginine, particularly preferably by arginine. The amino acid residue at (b) position 75 or at a position corresponding to this position is preferably substituted by alanine or arginine, particularly preferably by arginine. The amino acid residue at (c) position 142 or at a position corresponding to this position is particularly preferably substituted by lysine.

In the mutant prepro sequence of the alkaline protease of the present invention, substitution of amino acid residues may be performed at two or more positions selected from positions (a) through (c), so long as characteristics of the resultant enzyme do not vary. Specific examples of combinations of substitution of amino acid residues at two or more positions include Lys52(Asp/Arg)+Gln75(Ala/Arg), Lys52(Asp/Arg)+Glu142Lys, Lys52(Asp/Arg)+Glu142Lys, and Gln75(Ala/Arg)+Lys52(Asp/Arg)+Glu142Lys. Preferred combinations are Lys52 Arg+Gln75Arg, Lys52Asp+Gln75Ala, and Lys52Asp+Glu142Lys. The combination Lys52Arg+Glu142Lys is particularly preferred. Amino acids are designated by the three letters; the symbol “+” refers to the case where additional substitution is performed; and the symbol “/” refers to the case where either of the right and left two amino acids may be employed for substitution.

The alkaline protease of the present invention has the aforementioned mutant prepro sequence, and the alkaline protease, when in a mature form, has the amino acid sequence of SEQ ID NO: 2 or an amino acid sequence having a homology of 80% or higher to this amino acid sequence.

As the amino acid sequences having 80% or higher homology to the amino acid sequence of SEQ ID NO: 2, preferred are those having a homology of 87% or higher, more preferably 90% or higher, still more preferably 95% or higher, and even still more preferably 98% or higher. Such alkaline protease may be a wild-type alkaline protease or a variant. Preferably, the alkaline protease exhibits oxidant resistance, and has a molecular weight of 43,000±2,000 as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Preferably, the alkaline protease has the following characteristics: acting within an alkaline region at a pH of 8 or higher, exhibiting oxidant resistance, its enzymatic activity being not inhibited in the presence of a fatty acid of high concentration, exhibiting high gelatin-degrading activity, exhibiting at least 80% residual activity when treated at 50° C. and a pH of 10 for 10 minutes, being inhibited by diisopropyl fluorophosphate (DFP) and phenylmethanesulfonyl fluoride (PMSF), and having a molecular weight of 43,000±2,000 as determined by SDS-PAGE.

As used herein, the expression “the alkaline protease exhibits oxidant resistance” refers to the case where, after the alkaline protease is allowed to stand at 30° C. for 20 minutes in a 20 mM Britton-Robinson buffer (pH 10) containing hydrogen peroxide (50 mM) and calcium chloride (5 mM), the alkaline protease maintains at least 50% residual activity. So long as the alkaline protease maintains the aforementioned characteristics, the alkaline protease may be a wild-type, variant, or artificially mutated alkaline protease.

Examples of the alkaline protease having the amino acid sequence of SEQ ID NO: 2 (mature alkaline protease) include KP43 [derived from Bacillus sp. KSM-KP43 (FERM BP-6532), International Publication WO99/18218]. Examples of the alkaline protease having an amino acid sequence having a homology of 80% or higher to the amino acid sequence of SEQ ID NO: 2 include protease KP9860 (GenBank Accession No. AB046403) [derived from Bacillus sp. KSM-KP9860 (FERM BP-6534), International Publication WO99/18218]; protease 9865 (GenBank Accession No. AB084155) [derived from Bacillus sp. KSM-9865 (FERM P-1592), Japanese Patent Application No. 2002-002653]; protease E-1 (GenBank Accession No. AB046402) [derived from Bacillus No. D-6 (FERM P-1592), Japanese Patent Application Laid-Open (kokai) No. 49-71191]; protease Ya (GenBank Accession No. AB046404) [derived from Bacillus sp. Y (FERM BP-1029), Japanese Patent Application Laid-Open (kokai) No. 61-280268]; protease SD521 (GenBank Accession No. AB046405) [derived from Bacillus SD521 (FERM P-11162), Japanese Patent Application Laid-Open (kokai) No. 3-191781]; protease A-1 (GenBank Accession No. AB046406) [derived from NCIB12289, International Publication WO88/01293]; protease A-2 [derived from NCIB12513, International Publication WO98/56927]; a mutant obtained through substitution at position 46 of the amino acid sequence of SEQ ID NO: 2 by leucine; a mutant obtained through substitution at position 57 by alanine; a mutant obtained through substitution at position 103 by arginine; a mutant obtained through substitution at position 107 by lysine; a mutant obtained through substitution at position 124 by lysine or alanine; a mutant obtained through substitution at position 136 by alanine; a mutant obtained through substitution at position 193 by alanine; a mutant obtained through substitution at position 195 by asparagine, glutamic acid, arginine, proline, threonine, valine, histidine, serine, lysine, glutamine, methionine, cysteine, alanine, aspartic acid, tryptophan, glycine, or phenylalanine; a mutant obtained through substitution at position 247 by threonine or arginine; a mutant obtained through substitution at position 257 by valine; a mutant obtained through substitution at position 342 by alanine; a double-mutant obtained through substitution at positions 66 and 264 by aspartic acid and serine, respectively (Japanese Patent Application No. 2000-355166 (Japanese Patent Application Laid-Open (kokai) No. 2002-218989)); a mutant obtained through substitution at position 84 of the amino acid sequence of SEQ ID NO: 2 by arginine; a mutant obtained through substitution at position 104 by proline; a mutant obtained through substitution at position 256 by alanine or serine; a mutant obtained through substitution at position 369 by asparagine (Japanese Patent Application Laid-Open (kokai) No. 2002-306176); a mutant obtained through substitution at position 251 of the amino acid sequence of SEQ ID NO: 2 by asparagine, threonine, isoleucine, valine, leucine, or glutamine; a mutant obtained through substitution at position 256 by serine, glutamine, asparagine, valine, or alanine (Japanese Patent Application No. 2001-329472); and an alkaline protease having an amino acid sequence having a homology of 80% or higher, preferably 87% or higher, more preferably 90% or higher, still more preferably 95% or higher, to the amino acid sequences of the aforementioned proteases. FIGS. 2 a and 2 b show, in a side-by-side manner of representation, the amino acid sequences of some of the aforementioned alkaline proteases.

Cloning of the gene encoding the alkaline protease of the present invention may be performed by means of shotgun cloning, PCR, or the like. The thus-cloned gene may be subjected to mutagenesis. An example of the base sequence of the thus-obtained gene is shown as SEQ ID NO: 3. The gene encoding the prepro sequence of SEQ ID NO: 1 or a prepro sequence having a homology of 80% or higher to this prepro sequence may be cloned by means of PCR or the like.

Mutagenesis of the gene encoding the prepro sequence may be performed by means of random mutagenesis or site-directed mutagenesis, which is a customary technique. More specifically, mutagenesis of the gene may be performed by use of, for example, a Site-Directed Mutagenesis System Mutan-Super Express Km kit (Takara).

The method for producing the protease of the present invention by use of the thus-obtained mutant prepro gene will now be described. When the gene encoding the prepro sequence of the alkaline protease—the base sequence of the gene is shown in SEQ ID No: 3—is mutated, the resultant mutant gene is employed as is. Meanwhile, when the gene encoding a mature enzyme having an amino acid sequence having a homology of 80% or higher to the amino acid sequence of SEQ ID NO: 2 is ligated to the downstream region of the mutant prepro gene, a structural gene may be produced by providing an appropriate restriction enzyme cleavage site by means of site-directed mutagenesis or by employing recombinant PCR or the like. Subsequently, the mutant gene is introduced into a plasmid vector, and a host bacterium which can reliably amplify and maintain the vector is transformed. Alternatively, the mutant gene is introduced into chromosomal DNA of a host bacterium which can reliably maintain the gene. Examples of the host bacterium which satisfies the aforementioned requirements include bacteria belonging to the genus Bacillus, Escherichia coli, mold, yeast, and actinomycetes. The host bacterium containing the mutant gene is inoculated into a culture medium containing an assimilable carbon source, nitrogen source, and other essential nutrients, and cultured according to the customary method.

Thus, the alkaline protease having a prepro sequence of the present invention, which is expressed in the host cells, is effectively produced by the transformants.

As used herein, the expression “effectively produced” refers to the case where, when a mutant alkaline protease is produced under the same conditions as those employed for production of a non-mutated alkaline protease (for example, inoculation into a culture medium containing polypeptone S (8% (w/v)), yeast extract (0.3%), maltose (10%), magnesium sulfate heptahydrate (0.04%), potassium dihydrogenphosphate (0.2%), sodium carbonate anhydrate (1.5%), and tetracycline (30 ppm); and shaking the culture at 30° C. for three days), and the activity and the amount of protein in the culture supernatant are measured, the activity or amount of the protease is at a certain level or higher. For example, the expression “effectively produced” refers to the case where the activity or the amount of protein is increased by at least 5%, preferably at least 10%, more preferably at least 15% compared with that of parental alkaline protease. When variation in, for example, specific activity of the thus-produced alkaline protease is not confirmed, either the activity or amount of the protease may be measured.

The prepro sequence is cleaved out of the alkaline protease, and a mature enzyme is secreted outside the host cells. The mature enzyme may be collected and purified by means of usual methods for collecting and purifying enzymes. For example, the culture broth is subjected to centrifugation or filtration, to thereby remove the host cells, and the aimed enzyme is obtained from the culture supernatant by means of a customary purification technique. The thus-obtained enzyme solution may be employed without any treatment. Alternatively, the enzyme solution may be additionally subjected to purification, crystallization, powdering, or granulation by means of a known method.

The thus-obtained alkaline protease exhibits oxidant resistance, maintains casein-degrading activity even in the presence of a fatty acid of high concentration, and exhibits high gelatin-degrading activity. In addition, the alkaline protease preferably has a molecular weight of 43,000±2,000 as determined by SDS-PAGE, and beneficially exhibits activity within the alkaline region. Therefore, the alkaline protease can be employed in, for example, laundry detergents, bleaching agents, detergents for cleaning hard surfaces, detergents for drainpipes, denture-cleaning agents, and detergents for sterilizing medical apparatuses.

EXAMPLES Example 1

A DNA fragment of about 2.0 kb (including a termination codon) of the alkaline protease structural gene (SEQ ID NO: 3) derived from Bacillus sp. strain KSM-KP43 was subjected to random mutagenesis. Firstly, PCR was performed by use of BcaBEST Sequencing Primer RV-M (Takara) and BcaBEST Sequencing Primer M13-47 (Takara) which can amplify the aforementioned DNA of about 2.0 kb introduced into the multi-cloning site of pKF18k (Takara). The reaction was performed by the use of the template DNA (30 ng), each primer (20 pmol), each dNTP (20 nmol), appropriate amounts of manganese sulfate and dimethyl sulfoxide, Takara Taq-added reaction buffer (10 μL), and Taq polymerase (2.5 U) (total amount of these substances: 100 μL). The PCR was performed for 30 cycles, each cycle including 94° C.×one minute, 55° C.×two minutes, and 72° C.×three minutes, and the resultant PCR product was maintained at 72° C. for 10 minutes. The PCR product was purified by use of a High Pure PCR Product Purification kit (Roche), and eluted with sterile water (100 μL). The thus-obtained DNA fragment of about 2.0 kb was cleaved by BamHI and XbaI (Roche), and then mixed with pKF18k which had been treated with these enzymes, to thereby perform ligation by use of a DNA Ligation kit ver. 2 (Takara). Escherichia coli HB101 cells were transformed by use of the resultant reaction mixture, and grown on an LB agar medium containing kanamycin (100 μg/mL). The thus-obtained transformant was inoculated into an LB medium containing kanamycin (100 μg/mL), and subjected to shaking culture at 30° C. The activity of the resultant culture supernatant was measured by use of a synthetic substrate (Glt-Ala-Ala-Pro-Leu-pNA, Peptide Institute); a culture broth having an activity higher than that of the parental alkaline protease was selected; and PCR was performed under the same conditions as described above by use of a small amount of the strain, BcaBEST Sequencing Primer RV-M, and BcaBEST Sequencing Primer M13-47, to thereby amplify mutant genes. The thus-amplified gene fragments were purified, and the nucleotide sequence of each of the fragments was determined by use of a DNA Sequencer (model: 377, Applied Biosystems) employing an appropriate primer and a Big Dye DNA sequencing kit (Applied Biosystems).

As a result, a mutant exhibiting enhanced protease activity was found to be produced by expression of each of the mutant genes in which lysine at position 52, glutamine at position 75, and glutamic acid at position 142 of the amino acid sequence of SEQ ID NO: 1 were substituted by arginine, arginine, and lysine, respectively, and the protease activity of the mutant was found to be increased by 2 to 10%. Subsequently, the alkaline protease structural gene was subjected to mutation in order to confirm the effects of substitution of the amino acids at the above mutation positions by other amino acids. For mutagenesis, the amino acids at positions 52, 75, and 142 were substituted by arbitrary amino acids by use of a Site-Directed Mutagenesis System Mutan-Super Express Km kit (Takara). PCR was performed by the use of template plasmid (plasmid obtained through introduction of the protease structural gene into BamHI and XbaI sites of pKF18k) (30 ng), a selection primer attached to the kit, primers Nos. 3 through 5 (SEQ ID NOs: 5 through 7) (20 pmol for each), and Takara LA Taq. The reaction was performed for 30 cycles, each cycle including 94° C.×one minute, 55° C.×two minutes, and 72° C.×three minutes. The resultant PCR fragment was purified. Additionally, PCR was performed by use of the purified fragment serving as a primer, template plasmid (30 ng), and LA Taq. The reaction was performed for 30 cycles, each cycle including 94° C.×one minute, 55° C.×two minutes, and 72° C.×four minutes. The resultant PCR product was purified and subjected to ligation. Thereafter, Escherichia coli MV1184 strain was transformed by use of the PCR product. Plasmid DNA is extracted from the transformed strain, and Escherichia coli HB101 cells were transformed by use of the plasmid DNA. The transformant was inoculated into an LB medium containing kanamycin (100 μg/mL), and subjected to shaking culture at 30° C. The activity of the resultant culture supernatant was measured by use of a synthetic substrate, and a culture broth having an activity higher than that of the parental alkaline protease was selected. PCR was performed by use of the strain serving as a template, to thereby amplify mutant genes, and the amplified genes were purified. After purification, the nucleotide sequence of each of the genes was determined. As a result, the activities of the mutant in which lysine at position 52 was substituted by aspartic acid and the mutant in which glutamine at position 75 was substituted by alanine were found to be higher than that of the parental alkaline protease by 5% and 10%, respectively. A mutant in which the amino acid at position 142 was substituted by an amino acid other than lysine failed to exhibit enhanced protease activity.

Furthermore, the effect of combinations of the aforementioned mutation positions on enhancement of protease activity was investigated. A BamHI-XhoI fragment in which the amino acid at position 52 was mutated, an XhoI-AatII fragment in which the amino acid at position 142 was mutated, and an AatII-XbaI fragment containing the gene encoding a mature enzyme were prepared, and these fragments were mixed with pKF18k which had been treated with BamHI and XbaI, to thereby perform ligation. An Escherichia coli HB101 cells were transformed by the use of the resultant plasmid DNA, and a double-mutant containing the mutation Lys52Arg and the mutation Glu142Lys was produced through culture. As a result, the activity of the Lys52Arg+Glu142 Lys mutant was found to be higher than that of the Lys52Arg mutant by 10%.

Example 2

When KP43 protease was employed as the parental alkaline protease, each of the above-obtained mutant prepro sequences was found to have the effect of enhancing activity of the resultant mutant as described above. Further investigations were performed for confirming the effect of the prepro sequence of the present invention on the mutant alkaline protease exhibiting enhanced secretion and specific activity (alkaline protease KP43H obtained through the following substitution of the amino acid sequence of SEQ ID NO: 2:

Phe46Leu/Thr65Pro/Tyr195Gly/Val273Ile/Thr359Ser/ Asp369Asn/Ser387Ala).

The gene fragment encoding each of the mutant prepro sequences was cleaved out of pKF18k by the use of BamHI and AatII, and, by the use of ligase, the gene fragment was ligated to the gene encoding KP43H, which was cleaved out of pKF18k by the use of AatII and XbaI (the AatII site was newly produced through site-specific substitution of a nucleotide without changing the amino acid encoded by the gene). Escherichia coli HB101 cells were transformed by the use of the resultant plasmids. After being extracted, each of the plasmids was cleaved by the use of BamHI and XbaI. The resultant fragments were introduced into pHA64 which had previously been treated with these enzymes, and Bacillus sp. strain KSM-KP43 were transformed by means of electroporation employing SSH-10 (Shimadzu Corporation) and gene pulser cuvette (Bio-Rad). Introduction of the protease gene was determined on the basis of the generation of skim milk dissolution spots of transformants formed on a skim milk-containing alkaline agar medium [skim milk (Difco) (1% (w/v)), bactotryptone (Difco) (1%), yeast extract (Difco) (0.5%), sodium chloride (0.5%), agar (1.5%), sodium carbonate anhydrate (0.05%), and tetracycline (15 ppm)]. Transformants containing plasmids in which the protease gene was inserted into pHA64 were selected, and the strains were subjected to the below-described culture.

Single colony isolation and halo formation were confirmed in each of the transformants, and the strain was inoculated into a seed culture medium (5 mL) [polypeptone S (Nihon Pharmaceutical Co., Ltd.) (6.0% (w/v)), yeast extract (0.1%), maltose (1.0%), magnesium sulfate heptahydrate (0.02%), potassium dihydrogenphosphate (0.1%), sodium carbonate anhydrate (0.3%), and tetracycline (30 ppm)] in a test tube, followed by pre-culture at 30° C. and 320 rpm overnight. The resultant seed culture broth (1% (v/v)) was inoculated into a culture medium (20 mL) [polypeptone S (8% (w/v)), yeast extract (0.3%), maltose (10%), magnesium sulfate heptahydrate (0.04%), potassium dihydrogenphosphate (0.2%), sodium carbonate anhydrate (1.5%), and tetracycline (30 ppm)] in a Sakaguchi flask (capacity: 500 mL), followed by culture at 30° C. and 121 rpm for three days. The resultant culture broth was subjected to centrifugation, and the protease activity of the resultant culture supernatant was measured. The protease activity was measured by means of the casein method, and the amount of the resultant protein was measured by the use of a protein assay kit (Wako Pure Chemical Industries, Ltd.). As a result, the activity of the alkaline protease KP43H having the mutant prepro sequence was found to be increased by 5 to 25% compared with that of the control (a product produced through culture of a transformant having an alkaline protease KP43H gene under the aforementioned conditions) (Table 1). Plasmids were collected from the above-selected transformants, and the base sequence of each of the plasmids was determined. As a result, it was confirmed that the transformants were aimed mutant.

It was found that the alkaline protease produced by the use of the aforementioned mutant prepro sequence was produced in the transformant in an increased amount. In addition, it was also found that the alkaline protease exhibits the characteristics of the parental alkaline protease; specifically, exhibiting oxidant resistance, exhibiting high gelatin-degrading activity, its casein-degrading activity being not inhibited by a fatty acid of high concentration, having a molecular weight of 43,000±2,000 as determined by SDS-PAGE, and exhibiting activity within an alkaline region.

[Protease Assay—Synthetic Substrate Method]

A synthetic substrate (Glt-Ala-Ala-Pro-Leu-pNA: AAPL) was employed for the measurement of enzymatic activity. A solution containing a 100 mM borate buffer (pH 10.5) (48.5 μL) and 100 mM AAPL (1.5 μL) was added to a 96-well assay plate (Iwaki), and an appropriately diluted enzyme solution or culture broth (50 μL) was added thereto, to thereby initiate reaction at 30° C. for 15 minutes by the use of an iEMS Reader MS (LABSYSTEMS). The absorbance of liberated p-nitroaniline was measured at 414 nm. One unit of enzymatic activity was defined as the amount of the enzyme required for increasing the absorbance by 0.001 per minute under the above reaction conditions.

[Protease Assay—Casein Method]

A 50 mM borate buffer (pH 10.5) (1.0 mL) containing casein (1% (w/v)) was maintained at 30° C. for five minutes, and subsequently an enzyme solution (0.1 mL) was added to the buffer, to thereby allow reaction to proceed for 15 minutes. A reaction stopping solution (0.11 M trichloroacetic acid-0.22 M sodium acetate-0.33 M acetic acid) (2.0 mL) was added to the resultant reaction mixture, and the mixture was allowed to stand at room temperature for 30 minutes. Thereafter, the resultant mixture was subjected to filtration, and the amount of an acid-soluble protein in the resultant filtrate was measured by means of a modification of the method of Lowry, et al. Specifically, an alkaline copper solution (1% potassium sodium tartrate:1% copper sulfate pentahydrate:2% sodium carbonate-0.1 N sodium hydroxide=1:1:100) (2.5 mL) was added to the filtrate (0.5 mL), and the resultant mixture was allowed to stand at room temperature for 10 minutes. Subsequently, to the mixture was added a phenol solution [obtained by diluting a phenol reagent (Kanto Kagaku) two-fold with distilled water] (0.25 mL), and the resultant mixture was incubated at 30° C. for 30 minutes. Thereafter, the absorbance of the mixture was measured at 660 nm. One unit of protease activity (1 PU) was defined as the amount of the enzyme required for liberating acid-soluble protein degradation products equivalent to 1 mmol of tyrosine per minute under the above reaction conditions.

TABLE 1 Mutant Relative activity (%) KP43H (control) 100 Lys52Asp 105 Lys52Arg 119 Gln75Ala 110 Gln75Arg 110 Glu142Lys 107 Lys52Arg/Glu142Lys 125

Example 3

(1) Preparation of Detergent

Water (465 kg) was added to a mixing tank (1 m³) equipped with a stirring paddle. After the temperature of the water reached 55° C., a 40% (w/v) aqueous solution of sodium polyacrylate (135 kg) was added to the water. After the resultant mixture was stirred for 15 minutes, sodium carbonate (120 kg), sodium sulfate (60 kg), sodium sulfite (9 kg), and a fluorescent dye (3 kg) were added to the mixture. After the resultant mixture was stirred for additional 15 minutes, zeolite (300 kg) was added to the mixture, and then stirred for 30 minutes, to thereby yield a homogenous slurry (the water content of the slurry: 50 mass %). The slurry was sprayed through a pressure spray nozzle provided in the vicinity of the top of a spray-drying tower, to thereby yield a granular base (a high-temperature gas was fed at 225° C. through a lower part of the spray-drying tower, and discharged at 105° C. from the top of the tower).

Subsequently, the thus-obtained granular base (100 parts by mass) was fed to a Lodige mixer (product of Matsuzaka Giken Co., Ltd., capacity: 20 L, equipped with a jacket). While the granular base was stirred with the main shaft (150 rpm), a mixture of a nonionic surfactant (20 parts by mass), sodium linear alkyl (C10–C13) benzenesulfonate (22 parts by mass), a sodium salt of a fatty acid (C14–C18)(4 parts by mass), polyethylene glycol (2 parts by mass), and water (4 parts by mass) was added to the mixer over three minutes. Thereafter, the resultant mixture was stirred for five minutes. Furthermore, crystalline sodium silicate (20 parts by mass) and zeolite (10 parts by mass) were added to the mixer, to thereby perform surface coating and yield a detergent base.

The detergent base (99 mass %) was mixed with granules of the protease of the present invention (0.5 mass %) and a perfume (0.5 mass %), to thereby produce final granular detergent A.

(2) Raw Materials Employed

Nonionic surfactant: Emulgen 108 KM (average molar number of ethylene oxide added: 8.5, product of Kao Corporation)

Aqueous solution of sodium polyacrylate: average molecular weight: 10,000 (produced according to the method described in Examples of Japanese Patent Publication (kokoku) No. 2-24283)

Sodium carbonate: Dense ash (product of Central Glass Co., Ltd.)

Zeolite: Zeolite 4A (average particle size: 3.5 μm, product of Tosoh Corporation)

Polyethylene glycol: K-PEG6000 (average molecular weight: 8,500, product of Kao Corporation)

Crystalline sodium silicate: Powder SKS-6 (product of Hoechst Tokuyama Co., Ltd.)

Granules of the protease of embodiments of the present invention: granules (6 PU/g) prepared from each of the purified samples of the alkaline protease of embodiments of the present invention shown in Table 1 by use of the method described in Example 1 of Japanese Patent Application Laid-Open (kokai) No. 62-257990

Fluorescent dye: Tinopal CBS-X (product of Ciba-Geigy Corp.)

Example 4

(1) Preparation of Detergent

The slurry (solid content: 50 mass %) was spray-dried with hot air at 250° C., to thereby yield a granular base containing sodium polyacrylate (mass average molecular weight: 10,000) (7 mass %), sodium carbonate (26 mass %), sodium sulfate (20 mass %), sodium chloride (6 mass %), the fluorescent dye (0.5 mass %), zeolite (40 mass %), and water (0.5 mass %).

Subsequently, the thus-obtained granular base (100 parts by mass) was fed to a Lodige mixer (product of Matsuzaka Giken Co., Ltd., capacity: 20 L, equipped with a jacket). While the granular base was stirred with the main shaft (150 rpm), a mixture of a nonionic surfactant (20 parts by mass), sodium linear alkyl (C10–C13) benzenesulfonate (22 parts by mass), a sodium salt of a fatty acid (C14–C18)(4 parts by mass), polyethylene glycol (2 parts by mass), and water (4 parts by mass) was added to the mixer over three minutes. Thereafter, the resultant mixture was stirred for five minutes. Furthermore, crystalline sodium silicate (20 parts by mass) and zeolite (10 parts by mass) were added to the mixer, to thereby perform surface coating and yield a detergent base.

The detergent base (95 mass %) was mixed with bleaching agent granules (2.8 mass %), bleaching activator granules (1.2 mass %), granules of the protease of embodiments of the present invention (0.5 mass %) and a perfume (0.5 mass %), to thereby produce final granular detergent B.

(2) Raw Materials Employed

Nonionic surfactant: Emulgen 108 KM (average mole number of ethylene oxide added: 8.5, product of Kao Corporation)

Aqueous solution of sodium polyacrylate: average molecular weight: 10,000 (produced according to the method described in Examples of Japanese Patent Publication (kokoku) No. 2-24283)

Sodium carbonate: Dense ash (product of Central Glass Co., Ltd.)

Zeolite: Zeolite 4A (average particle size: 3.5 μm, product of Tosoh Corporation)

Polyethylene glycol: K-PEG6000 (average molecular weight: 8,500, product of Kao Corporation)

Crystalline sodium silicate: SKS-6 (product of Hoechst Tokuyama Co., Ltd.)

Granules of the protease of embodiments of the present invention: granules (6 PU/g) prepared from each of the purified samples of the alkaline protease of embodiments of the present invention shown in Table 1 according to the method described in Example 1 of Japanese Patent Application Laid-Open (kokai) No. 62-257990

Fluorescent dye: Tinopal CBS-X (product of Ciba-Geigy Corp.)

Bleaching agent granules: a sodium carbonate-hydrogen peroxide addition product (produced in a manner similar to that for producing bleaching agent granules described in paragraph [0019] of Japanese Patent Application Laid-Open (kokai) No. 2000-256699)

Bleaching activator granules: granules of sodium lauroyloxybenzenesulfonate (produced in a manner similar to that for producing bleaching activator granules described in paragraph [0018] of Japanese Patent Application Laid-Open (kokai) No. 2000-256699)

Example 5

Liquid detergent compositions (detergents C and D) shown in Table 2 were prepared.

TABLE 2 Detergent C Detergent D Components (mass %) (mass %) Nonionic surfactant¹⁾ 25.0  — Nonionic surfactant²⁾ 5.0 — Nonionic surfactant³⁾ 10.0  — Nonionic surfactant⁴⁾ — 9.0 Nonionic surfactant⁵⁾ — 9.0 Nonionic surfactant⁶⁾ — 2.5 Anionic surfactant⁷⁾ 1.0 — Silicone⁸⁾ — 0.8 Carboxylic acid-based polymer⁹⁾ 2.0 — Polymer¹⁰⁾ — 0.8 Citric acid 0.2 — Calcium chloride  0.05 — Monoethanolamine 4.0 — Triethylene glycol phenyl ether 3.0 — Propylene glycol 3.0 — Ethanol 2.0 2.0 Sodium sulfite 0.2 — Protease¹¹⁾ 0.5 1.0 Perfume 0.5 0.5 Water Balance Balance Total 100    100    Concentration upon use 20 g/30 L 40 g/30 L pH of liquid detergent 10.5  7.3 ¹⁾Polyoxyethylene (average molar number of EO added: 7) alkyl ether having an alkyl group derived from a C12–C14 secondary alcohol (Softanol 70, product of Nippon Shokubai Co., Ltd.) ²⁾Polyoxyethylene (average molar number of EO added: 12) alkyl ether having an alkyl group derived from a C12–C14 secondary alcohol (Softanol 120, product of Nippon Shokubai Co., Ltd.) ³⁾A product obtained by subsequently adding EO (average molar number: 5), PO (average molar number: 2), and EO (average molar number: 3) to a C10–C14 linear primary alcohol ⁴⁾Polyoxyethylene lauryl ether (average molar number of EO added: 8) ⁵⁾Polyoxyethylene lauryl ether (average molar number of EO added: 11.5) ⁶⁾Narrow range polyoxyethylene alkyl (sec-C₁₂/C₁₃) ether ⁷⁾Sodium linear alkyl (C10–C14) benzenesulfonate ⁸⁾Amide/ether-modified silicone polymer (BY16-906, product of Dow Corning Toray Silicone Co., Ltd.) ⁹⁾A phenoxypolyethylene glycol - acrylic acid - maleic acid copolymer synthesized according to the method described in lines 6 through 13 of page 11 of Japanese Patent Application Laid-Open (kokai) No. 10-60476 (mass average molecular weight: 10,000, solid content: 51.2%) ¹⁰⁾A sodium salt of a pentene/maleic acid (molar ratio: 50/50) copolymer (mass average molecular weight: 7,000) ¹¹⁾Each of the purified samples of the alkaline protease of embodiments of the present invention shown in Table 1 (15 PU/g)

Example 6

While sodium percarbonate and sodium carbonate (dense ash) of the components shown in the below-described Table 3 were mixed under stirring, a 40% aqueous solution of sodium polyacrylate, sodium linear alkyl benzenesulfonate or a nonionic surfactant, and sodium lauroyloxybenzenesulfonate were added to the mixture. Subsequently, to the resultant mixture was added granules of the protease of an embodiment of the present invention prepared according to the method described in Example 1 of Japanese Patent Application Laid-Open (kokai) No. 62-257990, and the resultant mixture was stirred so as to attain uniformity in the entirety of the mixture, thereby preparing a bleaching agent.

TABLE 3 Bleaching Bleaching agent E agent F Components (mass %) (mass %) Sodium percarbonate¹⁾ 72.0 72.0 Sodium carbonate (dense ash) 20.0 20.0 Anionic surfactant²⁾ 2.0 — Nonionic surfactant³⁾ — 2.0 Sodium polyacrylate⁴⁾ 1.0 1.0 Sodium lauroyloxybenzenesulfonate 4.0 4.0 Protease⁵⁾ 1.0 1.0 ¹⁾Particle size: 500 to 700 μm ²⁾Sodium linear alkyl (C12–C14) benzenesulfonate ³⁾Polyoxyethylene alkyl ether (number of carbon atoms of the alkyl group: 12 to 14, average molar number of EO added: 12) ⁴⁾Average molecular weight: 8,000 ⁵⁾Granules (6 PU/g) prepared from each of the purified samples of the alkaline protease of an embodiment of the present invention shown in Table 1 according to the method described in Example 1 of Japanese Patent Application Laid-Open (kokai) No. 62-257990

Example 7

Detergent compositions for an automatic dishwasher (detergents G and H) shown in the below-described Table 4 were prepared.

TABLE 4 Detergent G Detergent H Components (mass %) (mass %) Pluronic L-61¹⁾ — 4.0 Softanol EP-7085²⁾ 4.0 — Trisodium citrate — 30.0 Sodium tripolyphosphate 30.0 — Sodium percarbonate 20.0 20.0 Sodium carbonate 20.0 20.0 Amorphous silicate³⁾ 10.0 10.0 AA-MA⁴⁾ 4.0 4.0 Sodium sulfate 10.0 10.0 α-Amylase⁵⁾ 1.0 1.0 Protease⁶⁾ 1.0 1.0 ¹⁾A polyoxyethylene - polyoxypropylene copolymer (average molecular weight: 2,000) ²⁾A product obtained by adding to a C12–C14 sec-alcohol ethylene oxide (7 mol) and propylene oxide (8.5 mol) ³⁾JIS No. 2 sodium silicate ⁴⁾An acrylic acid - maleic acid copolymer ⁵⁾Duramyl 60T ™ (product of Novozymes) ⁶⁾Granules (6 PU/g) prepared from each of the purified samples of the alkaline protease of an embodiment of the present invention shown in Table 1 according to the method described in Example 1 of Japanese Patent Application Laid-Open (kokai) No. 62-257990

Example 8

A detergent composition for hard surfaces (detergent J) was prepared from components shown in the below-described Table 5.

TABLE 5 Components Detergent J (mass %) Anionic surfactant¹⁾ 15.0 Nonionic surfactant²⁾ 5.0 Nonionic surfactant³⁾ 5.0 Amphoteric surfactant⁴⁾ 7.5 Amphoteric surfactant⁵⁾ 4.0 Citric acid 1.0 Polypropylene glycol⁶⁾ 2.0 Ethanol 5.0 Protease⁷⁾ 1.0 Perfume, water, etc./pH adjusting agent 54.5 Total 100.0 ¹⁾Sodium polyoxyethylene (EOP = 4) alkyl (C12) ether sulfate ²⁾Polyoxyethylene (EOP = 8) alkyl (C12) ether ³⁾Alkyl (C12) polyglucoside (condensation degree: 1.3) ⁴⁾Mono long-chain tertiary alkyl (C12) dimethylamine oxide ⁵⁾Alkyl (C12) hydroxydimethyl sulfobetaine ⁶⁾Molecular weight: 10,000 ⁷⁾Each of the purified samples of the alkaline protease of an embodiment of the present invention shown in Table 1 (15 PU/mL)

Example 9

Granular detergents shown in the below-described Table 6 were prepared by using the aforementioned detergent A (see Example 3).

TABLE 6 Components (mass %) Detergent K Detergent L Detergent M Detergent N Detergent base 98.4 98.3 98.5 97.2 of Example 3 Perfume 0.5 0.5 0.5 0.5 Protease¹⁾ 0.5 0.5 0.5 0.5 Conventional 0.6 0.6 protease²⁾ Cellulase³⁾ 0.7 0.7 Lipase⁴⁾ 0.5 0.5 ¹⁾Granules (6 PU/g) prepared from each of the purified samples of the alkaline protease of an embodiment of the present invention shown in Table 1 according to the method described in Example 1 of Japanese Patent Application Laid-Open (kokai) No. 62-257990 ²⁾Protease K-16 described in Japanese Patent Application Laid-Open (kokai) No. 5-25492, the activity thereof being regulated to 5 PU/g by according to the method described in Example 1 of Japanese Patent Application Laid-Open (kokai) No. 62-257990 ³⁾KAC-500 (product of Kao Corporation) ⁴⁾Lipolase 100T ™ (product of Novozymes)

INDUSTRIAL APPLICABILITY

According to the present invention, an alkaline protease increased in production can be produced. In particular, there can be efficiently produced an alkaline protease having an activity even in the presence of a fatty acid of high concentration and exhibiting excellent detergency against complex soils containing proteins and sebum. 

1. An isolated DNA encoding an alkaline protease comprising a modified prepro amino acid sequence region and a mature alkaline protease amino acid sequence region wherein the unmodified prepro sequence is at least 95% homologous to SEQ ID NO:1 and said modified prepro amino acid sequence comprises one or more amino acid substitutions at positions corresponding to positions 52, 75, and 142 in the amino acid sequence set forth in SEQ ID NO:1 wherein said one or more substitutions improve the recovery of secreted and activated mature proteases fused to such a modified prepro region when the alkaline protease-encoding DNA is expressed in a Bacillus host cell and the substitutions are selected from the group consisting of; a substitution of aspartic acid or arginine for the amino acid at the position corresponding to position 52 of SEQ ID NO:1, a substitution of alanine or arginine for the amino acid at the position corresponding to position 75 of SEQ ID NO:1, and a substitution of lysine for the amino acid at the position corresponding to position 142 of SEQ ID NO:1, wherein said improved recovery is compared to the recovery obtained in the absence of said amino acid substitutions at positions corresponding to positions 52, 75, and 142 of SEQ ID NO:1, and wherein the mature alkaline protease amino acid sequence region comprises the amino acid sequence set forth in SEQ ID NO:2 or an amino acid sequence having at least 80% homology to the amino acid sequence set forth in SEQ ID NO:2.
 2. A recombinant vector comprising the DNA as recited in claim
 1. 3. A transformed bacterial host cell comprising the vector as recited in claim
 2. 4. The transformed host cell according to claim 3, wherein the host cell is a Bacillus host cell.
 5. An isolated DNA encoding a mutant prepro sequence comprising a modified prepro amino acid sequence region and a mature alkaline protease amino acid sequence region, wherein the unmodified prepro sequence is at least 95% homologous to SEQ ID NO:1 and said modified prepro amino acid sequence comprises one or more amino acid substitutions at positions corresponding to positions 52, 75, and 142 in the amino acid sequence set forth in SEQ ID NO:1 wherein said one or more substitutions improve the recovery of secreted and activated mature proteases fused to such a modified prepro region when the alkaline protease-encoding DNA is expressed in a Bacillus host cell and the substitutions are selected from the group consisting of: a substitution of aspartic acid or arginine for the amino acid at the position corresponding to position 52 of SEQ ID NO:1, a substitution of alanine or arginine for the amino acid at the position corresponding to position 75 of SEQ ID NO:1, and a substitution of lysine for the amino acid at the position corresponding to position 142 of SEQ ID NO:1, wherein said improved recovery is compared to the recovery obtained in the absence of said amino acid substitutions at positions corresponding to positions 52, 75, and 142 of SEQ ID NO:1.
 6. A method for producing an alkaline protease having the amino acid sequence of SEQ ID NO:2, or an amino acid sequence having at least 80% homology to the amino acid sequence set forth in SEQ ID NO:2, which method comprises culturing the transformed host cell as recited in claim 4 under conditions suitable for the expression of the protease and recovering the alkaline protease from the culture medium. 